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This is Hacker Public Radio episode 3,812 for Tuesday, the 14th of March 2023.

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Today's show is entitled, he pause computer does nothing.

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It is hosted by Brian in Ohio and is about 25 minutes long.

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It carries a clean flag.

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The summary is, a Z80 no-op test.

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Hello Hacker Public Radio, Brian in Ohio here.

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I'm out from under my rock doing part 2 of the Z80 computer build.

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As you can tell by the title, today's show is,

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peepos computer doesn't nothing.

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What that means, of course, if you don't know peepos, that's me,

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who my two-year-old grandson calls me peepo.

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He's the impetus, the reason that I'm doing this project

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and chronicling it here on HPR.

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So that maybe one day in the future, he or turns out

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his brothers in the oven, or maybe his cousin who's also in the oven.

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Maybe one of those three, or maybe all three,

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or who knows, will someday in the future,

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one or all of those kids will hang out with their old grandpa

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and learn how a computer works by building one themselves.

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So here I am, learning to do myself beforehand, getting ready.

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And so, in the last episode, I put together the one piece of test equipment

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that I needed, which was a logic probe, because I'm going to

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initially spool up this Z80 system using the facilities of an Arduino

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mega board to emulate, rom, and ram,

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and also to provide that some test equipment,

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like a logic probe, so I can program the system

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when I provide the required things to see if it's up and running.

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And so what's required initially is some power,

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clock signal, and some data.

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And the data I'm going to give it is,

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give the Z80 is provided by the Arduino mega board,

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which will be the machine code, which has the op code of zero.

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So the Z80 has about 180 instructions that it recognizes.

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They're all hexadecimal, coded, and it zero zero

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to the processor when it sees that.

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That's a no-op, it means do nothing and move on to the next instruction.

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And in this case, because the address lines aren't going to be hooked up to anything,

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they're not hooked up to any memory, it's just going to

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think that it's gone from one memory location to another,

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and it's just going to find another no-op.

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And so that's why this is called the no-op test.

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You're just getting the computer up and running,

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and having to do exactly nothing.

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So a couple things is to make sure just to clarify,

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I'm using an Arduino mega board, but it's not the Arduino environment.

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I'm running flash forth on it, and why would I use flash forth

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to do this instead of the Arduino environment,

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because flash forth is interactive.

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Without being a huge application in itself,

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there's other interactive languages that run on Arduino boards,

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things like circuit Python,

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but they're huge compared to the size of a fourth virtual machine.

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And also it's fourth is really geared towards manipulating things

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at the bare metal level, being able to dig into the registers

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and control whatever computer it's on at a very foundational level

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without any abstraction layers in between,

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except the ones you build yourselves by defining words.

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And why am I using them?

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They are doing a mega board instead of the Arduino unabored.

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It's because they're doing them, or yeah,

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instead of which has the mega 328 chip,

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and then has to do with the fact that the Arduino mega board

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has oooles and oooles of IO.

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It's got tons of ports, tons of available ports

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that I can manipulate to interact with the ZAD chip.

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It should be a snap to do it with this board.

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So the micro control board, like I said,

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is going to give the five volts the clock signal

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and the data to get the ZAD up and running.

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It's also going to provide the logic probe

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so we can test to see that it is running.

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So I wired up a probe shield that plugged into the board.

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First thing I did, and I've got pictures in the show notes

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to show all this stuff, is I hot glue to solder the spread board

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onto the Arduino mega probe shield, and then I plugged in the ZAD

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and the first wire that's shown by itself is a white wire

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that's the actual logic probe, that's from the last episode.

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I can plug that in onto the different pins of ZAD

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and see if things are happening or not.

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The next picture just shows power and brown being connected.

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I've split the power wire so I can have a rudimentary on-off switch.

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The next picture, there's a picture number 3

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with the blue wire that's a clock signal.

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And then the next one picture number 4 has got the show's yellow lines

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that are the control lines.

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The interrupt, the non-masculine interrupt, the white signal,

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the bus request and the reset signals.

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Those are all signals that are input to the ZAD

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to help control what's going on.

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Then orange wires are all the data bus.

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They go up to port A on the Arduino mega board.

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And the address lines then are, I put a little silver dot on the chip

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to show where pin 1 is.

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And so from where the clock chip is, which is pin 6,

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up and around clock wise, those unconnected pins are on the ZAD chip

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or all address lines.

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And the one that we're most interested in is the one at A0,

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which is next to the ground line, next to that black wire.

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And that's the one we'll be probing once we start this

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because what's as the ZAD goes through memory space,

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it's going to put each individual starting at zero

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and working up all the way up to 65,000

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binary 16-bit data addresses.

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And so that pin should be cycling between zero

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and one the most of all those pins.

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And so if I see activity on that pin,

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then I'm pretty confident that the chip is up and running.

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Now, so that's the hardware side of the test we're going to do today.

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On the software side, I fixed some of the fourth words

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in the last code that I presented in the last episode.

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It's kind of good HPR as a, it's always,

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it's good, it helps you to, when you post something

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and then even after the fact that I was looking at over and I saw

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that I made some mistakes and I refactored some of the words

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broken apart and I defined some new words,

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and that listing is in the show notes too.

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And so the fix I made was that the data processing word

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as defined was getting,

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when it, to sense that it was a static either higher or low signal,

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it was probing the wrong point.

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It was probing the output of pin H3 digital,

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six I think it is on the digital six on the,

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on the, on the, are doing a megabord.

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And what I really wanted to, you see,

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look at what was the input into pin E,

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the logic probe that, that white wire.

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So I changed that.

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I changed the, the output there too on the data processing word.

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I really don't care what frequency it is.

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So I just changed the word to, to just output if it's pulsing

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or just say it's pulsing, just put on the serial terminal pulse,

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the word pulse.

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Because I'm not interested in specific frequencies.

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I just put the clock in the logic and knit words,

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so that I can initialize the clock registers

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and on the, on the AVR chip.

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And I could, and the same for the logic probe, just,

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split in two words.

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I added some words to control the reset line.

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Those words are reset and run.

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Reset takes the, the pin, the reset pin from a high level state,

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which is in the run mode, and takes it to a low level state.

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So almost all control signals on the Z80 are active low.

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So when they're driven to ground, driven to zero voltage,

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they become active and do what they're supposed to do.

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So when you take the reset line and, and drive it to ground,

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then the, the chip is, is in a reset mode.

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And I added one more to, to be able to single step the clock.

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So I can, I can start and stop the clock with those words,

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start clock and stop clock.

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And I can change the frequency of the clock by, by,

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putting a number and, and then, calling the words set frequency.

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But I also wanted to be able to single step the, the, the, the,

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the Z80 chip.

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So that, we can probe around and look to see some other signals

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to see what's happening because the, the, like all computers,

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this Z80 has a very systematic way of functioning.

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And what it does is it, it, initially, it reads in from the data,

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looking, looks for, and it, it, and it interprets that first bit of data

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as, um, as some kind of instruction.

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And then if that instruction needs more data,

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it goes and fetches it, and then it processes it.

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And so the, you can, there's different signals that come alive in that process

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because each instruction for the Z80 takes between,

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I think it's like four in 20 clock cycles,

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depending on how long and how much data it needs.

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Um, so we, I've got the, uh, to, uh,

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I guess, uh, enough explanation I can do the test here.

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I've got the board plugged in.

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I've got, um, and I've got my serial term.

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I've got a, a little, uh, a serial term with serial terminal

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with a flash forth running at the flash forth prompt.

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And the first thing I'll do is I'll, uh,

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get the logic probe up and running by typing the word, um,

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logic probe, uh, in it.

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And why do that?

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It says, okay.

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Uh, and then I, uh, I'm going to, um,

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get the microtr, controller boards set up the ports on it.

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So that's, um, going to be, uh,

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let me look at my code.

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I can't remember exactly.

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Oh, Z80 ports in it.

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Basically what this does is it sets up those,

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those interconnections between the Z80 and the,

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and the, are doing a mega board up with all those wires.

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It, all those things that it's connected to,

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it's setting up them, them up correctly

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as either inputs or output ports.

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And so that is the word,

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Z80 ports in, uh, in it.

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And hit that, it's okay.

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And then, um, now add some power to the Z80 chip.

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And so I just, uh, plugged in five volts on the board.

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And now I should be able to, uh,

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the clock should be started.

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So I should be able to take my white logic probe

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and put it where the blue wire is.

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And I should be able to type the word sample in.

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And I'm expecting to see the word pulse output.

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And I do.

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And I can double check that that's actually working.

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I can go stop clock.

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Uh,

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this is the way I'm going to stop the clock.

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And now I'm going to do another sample of it of the pin.

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And, um, I'm in the wrong place.

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It's, uh,

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let's see here.

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Put this in to the right place.

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There you go.

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I should be able to get, um,

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let's see here.

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Seven.

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Okay, so I, uh,

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I had to, I never initialize the clock.

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I never typed in clock in it.

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So now I typed in clock in it,

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which, uh,

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initializes the clock.

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And now I can, uh,

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I can, um,

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I can, uh,

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start the clock.

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And I can sample.

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And, oops,

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different type quickly.

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Sample.

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It comes out pulse.

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And then I can stop the clock.

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And I can sample.

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And now it shows that it's a low.

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It's, it's not pulsing.

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It's a low signal.

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And I can start the clock again.

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And now,

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the next thing to probe is I'm going to take a,

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the logic probe wire that went wire out for more of the clock is the blue line.

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And I'm going to put it over in the A0 not line,

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which is that, that empty pin right next to the ground wire.

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And I'm going to, uh,

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sample there.

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And I need, and I get a high signal.

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So what I need to do is I need to properly reset the,

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the, the board, which I'll just type in the words reset and run.

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And then I should be able to sample.

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And I get a pulse.

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So the, so on the A0 pin, it's pulsing.

249
00:15:56,000 --> 00:16:00,000
And if I stop the clock.

250
00:16:00,000 --> 00:16:02,000
Oops, stop.

251
00:16:02,000 --> 00:16:05,000
If I type it correctly.

252
00:16:05,000 --> 00:16:07,000
Stop the clock.

253
00:16:07,000 --> 00:16:10,000
And now I sample.

254
00:16:10,000 --> 00:16:14,000
It's just a high because it's not, um,

255
00:16:14,000 --> 00:16:16,000
the clock stopped and you need a,

256
00:16:16,000 --> 00:16:18,000
a functioning clock for it to work.

257
00:16:18,000 --> 00:16:22,000
Um, so that to me is a good, uh,

258
00:16:22,000 --> 00:16:26,000
indication that the Z80 chip is, uh,

259
00:16:26,000 --> 00:16:28,000
behaving properly that it's, um,

260
00:16:28,000 --> 00:16:31,000
that the wiring and everything is connected correctly.

261
00:16:31,000 --> 00:16:33,000
And so now, uh, one other experiment,

262
00:16:33,000 --> 00:16:36,000
one other thing I can check is I can check the M1 line.

263
00:16:36,000 --> 00:16:40,000
M1 line is right next to the, um,

264
00:16:40,000 --> 00:16:43,000
well, I should make sure I've got, I've got a,

265
00:16:43,000 --> 00:16:46,000
uh, image of the, um,

266
00:16:46,000 --> 00:16:50,000
of the, uh,

267
00:16:50,000 --> 00:16:54,000
got the image of the Z80 chip,

268
00:16:54,000 --> 00:16:58,000
the pin out of the chip in the show notes.

269
00:16:58,000 --> 00:17:02,000
And yeah, M1 is actually, um,

270
00:17:02,000 --> 00:17:04,000
right next to reset.

271
00:17:04,000 --> 00:17:06,000
So, whatever.

272
00:17:06,000 --> 00:17:10,000
So the, the, um,

273
00:17:10,000 --> 00:17:13,000
the way is this, the,

274
00:17:13,000 --> 00:17:16,000
the order of things that happen when the Z80,

275
00:17:16,000 --> 00:17:19,000
uh, starts functioning when you first reset it.

276
00:17:19,000 --> 00:17:22,000
So what happens is we bring power up.

277
00:17:22,000 --> 00:17:26,000
You reset the, the, the Z80 puts it in no good state.

278
00:17:26,000 --> 00:17:30,000
It puts the program counter to zero.

279
00:17:30,000 --> 00:17:35,000
It puts address zero on the address bus.

280
00:17:35,000 --> 00:17:38,000
And then it, it, uh,

281
00:17:38,000 --> 00:17:42,000
it then draws M1 low.

282
00:17:42,000 --> 00:17:44,000
And M1 is just a signal.

283
00:17:44,000 --> 00:17:47,000
It, it draws the M1 signal low.

284
00:17:47,000 --> 00:17:49,000
And that's the indication,

285
00:17:49,000 --> 00:17:52,000
and it's starting the first part of what they call a machine cycle.

286
00:17:52,000 --> 00:17:55,000
Machine cycle is everything it takes to complete,

287
00:17:55,000 --> 00:17:58,000
uh, to get us in instruction,

288
00:17:58,000 --> 00:18:01,000
whatever data needs, and then finish it.

289
00:18:01,000 --> 00:18:03,000
And then, and then, uh,

290
00:18:03,000 --> 00:18:05,000
uh, it signals all this by first off,

291
00:18:05,000 --> 00:18:08,000
bringing them the M1 line low.

292
00:18:08,000 --> 00:18:12,000
And so the way to check that that's actually happening

293
00:18:12,000 --> 00:18:14,000
is to go back to that, uh,

294
00:18:14,000 --> 00:18:16,000
the terminal,

295
00:18:16,000 --> 00:18:19,000
and the clock is right now stopped.

296
00:18:19,000 --> 00:18:21,000
So I'm, I'm not going to start the clock.

297
00:18:21,000 --> 00:18:23,000
I'm going to single step the clock.

298
00:18:23,000 --> 00:18:25,000
And what I'm going to do is I'm going to,

299
00:18:25,000 --> 00:18:28,000
uh, go back to reset.

300
00:18:28,000 --> 00:18:33,000
I'm going to single step the, um,

301
00:18:33,000 --> 00:18:39,000
uh, just step, sorry step.

302
00:18:39,000 --> 00:18:42,000
I'm a single step, and then sample the pin.

303
00:18:42,000 --> 00:18:44,000
And I should see it high.

304
00:18:44,000 --> 00:18:48,000
And I'll do that a couple times, um,

305
00:18:48,000 --> 00:18:52,000
because it takes three clock cycles

306
00:18:52,000 --> 00:18:56,000
for the chip to be properly reset.

307
00:18:56,000 --> 00:18:58,000
So here we go.

308
00:18:58,000 --> 00:19:01,000
I'll do that one more time.

309
00:19:01,000 --> 00:19:05,000
And now I'm going to put the reset line

310
00:19:05,000 --> 00:19:07,000
into the run mode.

311
00:19:07,000 --> 00:19:11,000
And now I'm going to single step again and sample.

312
00:19:11,000 --> 00:19:14,000
And the M1 signal pin is still high,

313
00:19:14,000 --> 00:19:16,000
that clock signal.

314
00:19:16,000 --> 00:19:19,000
And now one more clock signal.

315
00:19:19,000 --> 00:19:23,000
And now when low, it's the beginning of a machine cycle.

316
00:19:23,000 --> 00:19:26,000
And if I click clock at a couple of times,

317
00:19:26,000 --> 00:19:28,000
it'll go back to high.

318
00:19:28,000 --> 00:19:33,000
And so I know that the, the M1 signal is working.

319
00:19:33,000 --> 00:19:35,000
And so with the A, uh,

320
00:19:35,000 --> 00:19:39,000
the address zero pulsing, um,

321
00:19:39,000 --> 00:19:42,000
that it, that it has busy, that it has activity on the address bus.

322
00:19:42,000 --> 00:19:46,000
And with the M1 signal cycling the way it is,

323
00:19:46,000 --> 00:19:50,000
I'm pretty confident that, uh, this is the 80 chip is, is good.

324
00:19:50,000 --> 00:19:54,000
And that, uh, it was a good, uh, a good, uh,

325
00:19:54,000 --> 00:19:58,000
no optest for that, uh, for that chip.

326
00:19:58,000 --> 00:20:00,000
And so I think that, uh, covers,

327
00:20:00,000 --> 00:20:02,000
I'm going to look my notes here.

328
00:20:02,000 --> 00:20:06,000
Uh, uh, uh, uh.

329
00:20:06,000 --> 00:20:10,000
Yeah, um, oh, there was one more thing we can do.

330
00:20:10,000 --> 00:20:13,000
And, and then that'll, that'll be the end.

331
00:20:13,000 --> 00:20:17,000
The last, uh, the last, uh,

332
00:20:17,000 --> 00:20:19,000
the last signal to probe.

333
00:20:19,000 --> 00:20:23,000
And this one is going to be, uh, the halt signal.

334
00:20:23,000 --> 00:20:27,000
When the, uh,

335
00:20:27,000 --> 00:20:29,000
when the, uh,

336
00:20:29,000 --> 00:20:31,000
uh,

337
00:20:31,000 --> 00:20:33,000
Z80 interrupts, uh,

338
00:20:33,000 --> 00:20:36,000
when the Z80 encounters a halt signal,

339
00:20:36,000 --> 00:20:39,000
it actually halts this, the processor,

340
00:20:39,000 --> 00:20:44,000
and does no opts internally until it receives an interrupt signal.

341
00:20:44,000 --> 00:20:48,000
And the halt signal, again, is active, um,

342
00:20:48,000 --> 00:20:50,000
believe it's active low.

343
00:20:50,000 --> 00:20:55,000
Also, and it's on pin number 18 of the chip.

344
00:20:55,000 --> 00:20:58,000
So I'm going to put it with the logic probe into,

345
00:20:58,000 --> 00:21:02,000
pin 18, and, um,

346
00:21:02,000 --> 00:21:04,000
do the same exact process.

347
00:21:04,000 --> 00:21:06,000
I'm going to reset the chip.

348
00:21:06,000 --> 00:21:10,000
So, uh, start with, uh, by putting it in,

349
00:21:10,000 --> 00:21:12,000
I put it in reset.

350
00:21:12,000 --> 00:21:15,000
And then I will, um,

351
00:21:15,000 --> 00:21:18,000
cycle the clock, uh,

352
00:21:18,000 --> 00:21:22,000
and sample a few times here.

353
00:21:22,000 --> 00:21:25,000
And now this time what it's going to be different is I'm going to put

354
00:21:25,000 --> 00:21:33,000
the, uh, hex address of 76, hex 76 on the data bus.

355
00:21:33,000 --> 00:21:36,000
Uh, and so, so when I start, uh,

356
00:21:36,000 --> 00:21:38,000
when I start to run the program,

357
00:21:38,000 --> 00:21:42,000
instead of finding on the data bus at address zero,

358
00:21:42,000 --> 00:21:43,000
a,

359
00:21:43,000 --> 00:21:43,000
a,

360
00:21:43,000 --> 00:21:46,000
a machine instruction zero,

361
00:21:46,000 --> 00:21:49,000
it's going to, the Z80's going to find on the data bus,

362
00:21:49,000 --> 00:21:52,000
the machine instruction 76, which is halt.

363
00:21:52,000 --> 00:21:53,000
And when it does that,

364
00:21:53,000 --> 00:21:56,000
I should, we should see when I sample that pin,

365
00:21:56,000 --> 00:21:57,000
the, the halt signal,

366
00:21:57,000 --> 00:21:59,000
it should go low.

367
00:21:59,000 --> 00:22:00,000
So let's do that.

368
00:22:00,000 --> 00:22:01,000
Let's put, uh,

369
00:22:01,000 --> 00:22:04,000
76 into, um,

370
00:22:04,000 --> 00:22:05,000
um,

371
00:22:05,000 --> 00:22:06,000
the data port.

372
00:22:06,000 --> 00:22:10,000
And I do that by typing in 76 data,

373
00:22:10,000 --> 00:22:11,000
uh,

374
00:22:11,000 --> 00:22:12,000
dollar sign 76,

375
00:22:12,000 --> 00:22:15,000
which is the hex notation in fourth for hex numbers,

376
00:22:15,000 --> 00:22:17,000
dollar sign 76.

377
00:22:17,000 --> 00:22:19,000
And then the word data,

378
00:22:19,000 --> 00:22:20,000
which is the data port,

379
00:22:20,000 --> 00:22:22,000
and I'm going to do C store,

380
00:22:22,000 --> 00:22:24,000
which is C and an exclamation point.

381
00:22:24,000 --> 00:22:28,000
That'll store the number 76 onto the data port.

382
00:22:28,000 --> 00:22:31,000
And I got the wrong thing.

383
00:22:31,000 --> 00:22:32,000
What's it called?

384
00:22:32,000 --> 00:22:33,000
May I got the wrong word?

385
00:22:33,000 --> 00:22:34,000
The wrong thing.

386
00:22:34,000 --> 00:22:36,000
It's called, um,

387
00:22:36,000 --> 00:22:38,000
what's it called?

388
00:22:38,000 --> 00:22:40,000
Yeah.

389
00:22:40,000 --> 00:22:42,000
Oh, it's couples,

390
00:22:42,000 --> 00:22:43,000
uh,

391
00:22:43,000 --> 00:22:44,000
case sensitive,

392
00:22:44,000 --> 00:22:45,000
fourth is,

393
00:22:45,000 --> 00:22:47,000
this fourth is case sensitive.

394
00:22:47,000 --> 00:22:49,000
So 76,

395
00:22:49,000 --> 00:22:51,000
capital DATA,

396
00:22:51,000 --> 00:22:53,000
C store,

397
00:22:53,000 --> 00:22:55,000
uh,

398
00:22:55,000 --> 00:22:57,000
C store,

399
00:22:57,000 --> 00:22:58,000
the values,

400
00:22:58,000 --> 00:23:02,000
the hex values 76 into the data port.

401
00:23:02,000 --> 00:23:03,000
And I get OK.

402
00:23:03,000 --> 00:23:05,000
And now I'm going to,

403
00:23:05,000 --> 00:23:06,000
uh,

404
00:23:06,000 --> 00:23:07,000
sample,

405
00:23:07,000 --> 00:23:08,000
and,

406
00:23:08,000 --> 00:23:09,000
uh,

407
00:23:09,000 --> 00:23:10,000
step and sample,

408
00:23:10,000 --> 00:23:11,000
the clock.

409
00:23:11,000 --> 00:23:13,000
And because it's,

410
00:23:13,000 --> 00:23:14,000
it's nothing there.

411
00:23:14,000 --> 00:23:15,000
OK.

412
00:23:15,000 --> 00:23:16,000
Now I'm going to,

413
00:23:16,000 --> 00:23:17,000
put the,

414
00:23:17,000 --> 00:23:19,000
the Z80 into run mode.

415
00:23:19,000 --> 00:23:22,000
And now I'm going to step and sample.

416
00:23:22,000 --> 00:23:25,000
And do it a few times to,

417
00:23:25,000 --> 00:23:28,000
because it'll take about four or five or six to get there.

418
00:23:28,000 --> 00:23:29,000
And there are now,

419
00:23:29,000 --> 00:23:30,000
the,

420
00:23:30,000 --> 00:23:31,000
the pin,

421
00:23:31,000 --> 00:23:32,000
uh,

422
00:23:32,000 --> 00:23:33,000
20,

423
00:23:33,000 --> 00:23:35,000
the signal on pin,

424
00:23:35,000 --> 00:23:35,000
uh,

425
00:23:35,000 --> 00:23:38,000
18 went from high to low.

426
00:23:38,000 --> 00:23:39,000
And that to me,

427
00:23:39,000 --> 00:23:40,000
uh,

428
00:23:40,000 --> 00:23:42,000
because it found that 76 on the,

429
00:23:42,000 --> 00:23:43,000
uh,

430
00:23:43,000 --> 00:23:44,000
on the data bus,

431
00:23:44,000 --> 00:23:47,000
it executed the instruction halt.

432
00:23:47,000 --> 00:23:48,000
And now this,

433
00:23:48,000 --> 00:23:49,000
the,

434
00:23:49,000 --> 00:23:50,000
um,

435
00:23:50,000 --> 00:23:53,000
uh,

436
00:23:53,000 --> 00:23:54,000
the Z80 is in a halt mode.

437
00:23:54,000 --> 00:23:55,000
So if I,

438
00:23:55,000 --> 00:23:56,000
if I,

439
00:23:56,000 --> 00:23:57,000
if I start the clock now,

440
00:23:57,000 --> 00:24:00,000
I'm going to do a nice sample.

441
00:24:00,000 --> 00:24:02,000
It should stay low.

442
00:24:02,000 --> 00:24:03,000
It should stay low.

443
00:24:03,000 --> 00:24:04,000
It should stay low.

444
00:24:04,000 --> 00:24:05,000
The,

445
00:24:05,000 --> 00:24:06,000
now completely,

446
00:24:06,000 --> 00:24:08,000
and a little stay low until I reset it,

447
00:24:08,000 --> 00:24:09,000
uh,

448
00:24:09,000 --> 00:24:10,000
or give it an interrupt signal,

449
00:24:10,000 --> 00:24:11,000
which I'm not going to do.

450
00:24:11,000 --> 00:24:12,000
And so there we go.

451
00:24:12,000 --> 00:24:13,000
Uh,

452
00:24:13,000 --> 00:24:15,000
Looks like I've got a functioning,

453
00:24:15,000 --> 00:24:15,000
uh,

454
00:24:15,000 --> 00:24:17,000
good does the 80 chip.

455
00:24:17,000 --> 00:24:17,000
I,

456
00:24:17,000 --> 00:24:19,000
have learned a little bit.

457
00:24:19,000 --> 00:24:21,000
It's about how to,

458
00:24:21,000 --> 00:24:22,000
um,

459
00:24:22,000 --> 00:24:23,000
manipulate,

460
00:24:23,000 --> 00:24:24,000
and a couple of instructions,

461
00:24:24,000 --> 00:24:25,000
the no-op instruction,

462
00:24:25,000 --> 00:24:26,000
and the halt instruction,

463
00:24:26,000 --> 00:24:28,000
and put them on the data bus,

464
00:24:28,000 --> 00:24:29,000
and,

465
00:24:29,000 --> 00:24:30,000
and get the,

466
00:24:30,000 --> 00:24:31,000
uh,

467
00:24:31,000 --> 00:24:32,000
Z80 to respond accordingly.

468
00:24:32,000 --> 00:24:34,000
And I was able to,

469
00:24:34,000 --> 00:24:35,000
uh,

470
00:24:35,000 --> 00:24:36,000
um,

471
00:24:36,000 --> 00:24:38,000
see all those things by,

472
00:24:38,000 --> 00:24:40,000
using the logic probe that's,

473
00:24:40,000 --> 00:24:42,000
that it's built into the,

474
00:24:42,000 --> 00:24:44,000
software on the,

475
00:24:44,000 --> 00:24:45,000
our degree.

476
00:24:45,000 --> 00:24:46,000
So,

477
00:24:46,000 --> 00:24:49,000
consider,

478
00:24:49,000 --> 00:24:50,000
consider this,

479
00:24:50,000 --> 00:24:51,000
uh,

480
00:24:51,000 --> 00:24:52,000
a successful experiment.

481
00:24:52,000 --> 00:24:53,000
Um,

482
00:24:53,000 --> 00:24:54,000
I think,

483
00:24:54,000 --> 00:24:55,000
uh,

484
00:24:55,000 --> 00:24:56,000
I'm not sure where to go from here.

485
00:24:56,000 --> 00:24:58,000
I think the next thing to do would be to,

486
00:24:58,000 --> 00:24:59,000
maybe do a,

487
00:24:59,000 --> 00:25:00,000
a more,

488
00:25:00,000 --> 00:25:01,000
um,

489
00:25:01,000 --> 00:25:02,000
a more,

490
00:25:02,000 --> 00:25:04,000
a longer set of instructions,

491
00:25:04,000 --> 00:25:05,000
a small program,

492
00:25:05,000 --> 00:25:06,000
and,

493
00:25:06,000 --> 00:25:07,000
uh,

494
00:25:07,000 --> 00:25:08,000
maybe even,

495
00:25:08,000 --> 00:25:09,000
I might have to add some LEDs or something.

496
00:25:09,000 --> 00:25:10,000
We'll see,

497
00:25:10,000 --> 00:25:13,000
or at least put out some numbers on to the,

498
00:25:13,000 --> 00:25:14,000
serial ports,

499
00:25:14,000 --> 00:25:16,000
like we can see get some output that way.

500
00:25:16,000 --> 00:25:17,000
And,

501
00:25:17,000 --> 00:25:17,000
um,

502
00:25:17,000 --> 00:25:19,000
and that'll require emulating,

503
00:25:19,000 --> 00:25:20,000
emulating some RAM.

504
00:25:20,000 --> 00:25:21,000
I think I'm,

505
00:25:21,000 --> 00:25:21,000
excuse me,

506
00:25:21,000 --> 00:25:22,000
a ROM,

507
00:25:22,000 --> 00:25:24,000
emulating some read-only memory.

508
00:25:24,000 --> 00:25:25,000
So I'll be the next,

509
00:25:25,000 --> 00:25:26,000
uh,

510
00:25:26,000 --> 00:25:28,000
the next step in this project.

511
00:25:28,000 --> 00:25:29,000
So,

512
00:25:29,000 --> 00:25:29,000
um,

513
00:25:29,000 --> 00:25:30,000
thanks for listening.

514
00:25:30,000 --> 00:25:31,000
Um,

515
00:25:31,000 --> 00:25:33,000
if you have any questions or comments,

516
00:25:33,000 --> 00:25:35,000
go ahead and leave them in the show notes,

517
00:25:35,000 --> 00:25:36,000
or you can email me.

518
00:25:36,000 --> 00:25:37,000
And if you,

519
00:25:37,000 --> 00:25:38,000
um,

520
00:25:38,000 --> 00:25:40,000
or if you're interested in this project,

521
00:25:40,000 --> 00:25:42,000
and if you, um,

522
00:25:42,000 --> 00:25:43,000
or if you're interested in retro computers,

523
00:25:43,000 --> 00:25:45,000
or doing something like this yourself,

524
00:25:45,000 --> 00:25:46,000
uh,

525
00:25:46,000 --> 00:25:48,000
pick up a mic and start recording a show,

526
00:25:48,000 --> 00:25:50,000
and upload it to HackerPublicRadio.

527
00:25:50,000 --> 00:25:52,000
And,

528
00:25:52,000 --> 00:25:53,000
if you,

529
00:25:53,000 --> 00:25:54,000
um,

530
00:25:54,000 --> 00:25:55,000
and anyway,

531
00:25:55,000 --> 00:25:56,000
thanks for listening.

532
00:25:56,000 --> 00:25:58,000
I appreciate your attention.

533
00:25:58,000 --> 00:26:00,000
And I just like to remind everybody,

534
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that it's not how much an item costs.

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It's how much you save.

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Goodbye.

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You have been listening to HackerPublicRadio,

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at HackerPublicRadio.org.

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Today's show was contributed by a HPR listening like yourself,

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if you ever thought of recording podcast,

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and click on our contribute link to find out how easy it means.

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Hosting for HPR has been kindly provided by an onsthost.com,

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On this otherwise stages,

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